# Questions tagged [rf]

Short for Radio Frequency, i.e. frequencies at which radiation (intentional or not) plays a role. Typically associated with wireless communications, but also relevant for high-speed PCB design.

4,015 questions
Filter by
Sorted by
Tagged with
1k views

### Do radios need a minimum range to function properly?

I'm going to use some well-known radios (nRF24L01+) to wirelessly read some voltage/current sensor data over little distances on a quad-copter since the drone is quite populated and we don't want to ...
• 2,099
3k views

### Is there a limit to how much power could be transmitted wirelessly?

This question kind of goes back to Nikolas Tesla's ambitious project of transmitting power wirelessly. I know that project failed for multiple reasons, but my question is more straight forward. I know ...
• 119
47 views

### Calculating dimentions of impedance-matched pads on PCB in an RF circuit

I am trying to build an RF amplifier based on an existing design. In my first version of PCB I didn't pay attention to solder pads of the RF transistor (BLF6G21) which were quite large on my reference ...
1 vote
39 views
+50

### Derive S-Parameter Matrices for Interconnected Multi-Port Networks of Arbitrary Size

Question(s) Is the math below correct? If not, then what should be changed? If you know of an authoritative reference for this derivation, then please post it in an answer, or in the comments. ...
• 2,160
43 views

### Purpose of trace pattern on RF PCB [duplicate]

When looking at a front-end PCB in 7 GHz spectrum analyzer I did see a multitude of trace patterns that I did not understand the purpose of. For example, the ones seen in the image below. Can anyone ...
1 vote
51 views

### Why can't the RF impedance be adjusted to 50 Ω？

I designed a PCB for UWB which use the NXP's NCJ29D6, and when I get the PCBA, I started to match the impedance of port of NCJ29D6 at 8 GHz. However, I found it is hard to pull the impedance from the ...
34 views

### Heising Modulation Reactor Inductance [closed]

I am trying to build a simple 5W tube Radio AM transmitter using Heising modulation. There is one thing I don't understand though. Does the inductance of the Heising reactor matter as long as it's ...
74 views

### Is it possible to connect two grounded coplanar waveguides?

On my PCB I have an SMA connector that delivers RF voltage signal (1MHz to 1GHz) from my Arbitrary Waveform Generator (AWG) to my device under test (DUT). The DUT is an IC, wirebonded to my PCB, and ...
1 vote
39 views

### EM simulation of antenna in battery proximity using QUCS studio

Have you tried simulating the behaviour of a commercial IoT antenna with Lithium Ion batteries in proximity using QUCS studio? I looked for tutorials but was not able to find anything useful. Can ...
• 554
1 vote
45 views

### How to Accurately Simulate a Wideband Bias Tee in LTSpice?

I'm currently working on designing a wideband bias tee and have been using LTSpice to simulate its performance. However, the results I'm obtaining seem too good to be true, and I'm concerned there ...
91 views

### Alternatives to SMA connectors in multiple-channel RF applications

I have a circuit with multiple input channels (~10-20), where to each channel I am applying RF voltage signals, usually sine waves, with varying frequency in the range of 1MHz to 1GHz and 0-5V peak-to-...
69 views

### Simple circuit to compare the phase of 2 identical RF signals (no demod) tuned to the FM band?

For obvious reasons, the enormous array of radio components for the commercial bands all presume demodulation of the radio frequency for audio. But, for a physics experiment testing the special ...
• 269
571 views

### What's a good way to connect an antenna to a breadboard for experimenting?

What's a good way to connect an antenna to a breadboard for experimenting? I am experimenting with RF (HF - 7 MHz) circuits and will be ready to connect an antenna to the breadboard soon. I intend to ...
• 1,307
87 views

### Can radio waves be focused to a point using a phased array?

I've seen many examples of ultrasonic phased arrays being used with non-linear phase relationship between elements to concentrate all the power at a specific point, for example here:              ...
• 107
1 vote
75 views

### Frequency of Oscillators

Greetings to the community, Recently I have been tinkering with FM transmitters/receivers, and as such have become familiar with many different oscillatory circuits. One thing that stood out to me is ...
87 views

### Is there a static capacitance between the metals in coaxial cables and other metals in the environment (or at infinity)?

In a coaxial cable, we are familiar with the capacitance per unit length between the two metal conductors, which is given by C=(2pi epsilon)/log(r/R). However, in my circuit design, the static mutual ...
100 views

### Communicating 1/4 miles without Wi-Fi. (I want to design a driveway alarm.) [closed]

We live in a very rural area of Ohio. Our driveway is 0.25 miles (400 m) long. I would like to design an alarm that will alert us when someone turns into our driveway. The easy part is the optical ...
• 101
914 views

### How do RF broadcast towers switch so much power so quickly?

Edit: I modified numbers below for a "licensed 1000 kW ERP channel", for which total true radiated power (being in a pancake shape since there is no need to radiate up into space) is ...
• 634
57 views

### rf question from razavi [closed]

I have a question about this example, I don't understand why the AM part is canceled while the other one isn't. Can somebody explain it in detail?
• 21
65 views

### SMA connector, PCB, straight, with differential signal

Good evening, I am designing a PCB that features a dipole antenna, of the same type we see on routers and about 6cm long (lambda/2 of 2.4GHz). In particular it is a rubber dipole whose interior looks ...
128 views

### High Insertion Loss on 4 Layer 5.8 GHz Board

I've built a board to serve as the front end of a 5.8 GHz Wi-Fi radio. The boards were built using OSH Park's 4-layer service, which uses ISOLA FR408-HR. It seems like these boards should be ...
• 571
103 views

### If ESR for a capacitor is not given, can you use f, C, and Q to calculate it?

To calculate ESR when it is not given, can you use the $Q$ value as follows? According to Wikipedia, dissipation factor relates $Q$, $\text{ESR}$, and $\tan(\delta)$ as follows:  \frac{1}{Q} ...
• 2,160
63 views

### Can we use telescopic antenna for RF receivers? [closed]

Can we use TE antenna for receiver? Because I have seen that TE antenna is used in transmitters and for receivers spring coil antenna is used. The reason that I have asked this question is I have seen ...
• 27
59 views

### Injecting bits to a parallel communication bus possible?

Antennas can recieve data (bits) because RF signals induce an analog signal into it in a serial format, essentially a voltage that varies over time. My question is can we have an antenna that can ...
• 15
80 views

### Visualizing 2 Layer PCB Return Currents

Hobbyist moving a manhattan-style prototype of an analog FM radio to a PCB for ease of assembly and access to SMT parts. I have attempted a 2 layer FR4 board with a 1.6mm thickness, as I feel that ...
1 vote
73 views

### Why do direct conversion receivers amplify only after mixing?

The vast majority of the simple direct conversion receivers I've seen amplify only after mixing. The RF is filtered before mixing, but not amplified at all. For example (from Solid State Design for ...
• 1,307
38 views

### Unable to replicate Twisted IFA antenna S-parameter curve using ANSYS HFSS 15

I am attempting to replicate the S-parameter curve for an antenna design as described in the paper "Antenna Design and Analysis" with DOI: 10.1109/LAWP.2009.2015345 using ANSYS HFSS 15. Here ...
• 31
56 views

### What is the purpose of this table on RF remote controls?

On most of the RF remote controls we can see this table. Can you explain what it means?
• 27
57 views

### What is the optimal way to place a BNC connection point on a printed circuit board?

I am working on my first RF project and I have two signals coming onto my board through a BNC connection. I have selected this BNC but their data sheet is not very informative. https://www.digikey.com/...
• 35
13 views

### ideal N-port Touchstone spec

Want to specify ideal i.e. frequency independent S-parameter N-port components in Touchstone file (v1 or v2), for import into circuit simulator. The official specs don't mention how many frequency ...
34 views

### Where should I take the measurement from to find the correct attenuation level of a resistive pi attenuator?

I am currently designing a resistive attenuator for an RF project I'm working on. I wanted to have several resistance combinations to obtain various attenuation levels (1-8 dBs). When I calculate the ...
32 views

### Modeling a short 10mm wire for RF

This is related to another question of mine looking for parasitics which need to be added to prevent oscillations in simulations . How should I model a short 10nH wire (say AWG 20 with 0.8 mm diameter ...
• 634
1 vote
62 views

### Can this oscillator possibly work?

I am trying to build a crude RF oscillator. My first attempt, though it simulated fine, disappointingly did not oscillate when soldered together. So, to debug this, I reduced the simulation example ...
• 634
59 views

### How can I simulate an RF signal as received by an antenna in LTspice?

How can I simulate an RF signal as received by an antenna in LTspice? I am designing a simple HF RF receiver and want to test it via LTspice. Can I simulate an RF signal as: A pure voltage source, ...
• 1,307
77 views

### RF jammer module power measurement using a spectrum analyzer

I have an RF jammer module that works at 2390-2510 MHz. The voltage is 24-28 V and it can transmit up to 50 W. When I use a spectrum analyzer, the value is around -20 dBm. If I'm not mistaken, -20 ...
96 views

### 12 channel remote control: 4-pin IC for 12 buttons: How?

This RF remote control uses ev1527 encoder. Although this IC has just 4 pins for buttons, this remote control has 12 buttons. How they have done such thing?
• 27
51 views

### Piezo tr switch no echo signal

I set this circuit to use piezo as transceiver. I can perfectly transfer the transmitter signal (10 burst pulse) but as transmitter still connected onto piezo , any reveived signal is disappears. When ...
1 vote
59 views

### MICRF112: loop vs monopole antenna

I'm designing a PCB that trasmit over 433 MHz with MICRF112. The datasheet says that the device works with monopole or loop antennas. I decided to go with a monopole antenna. This is the example ...
• 134
1 vote
145 views

### Will this FM transmitter work?

I found this schematic on circuit digest. I have tried to simulate it in LTspice. That's the wave I got from the simulation. Most of time it's just DC and does not oscillate at all. Is this going to ...
• 923
52 views

### How can I slow down the rise and fall time of a power MOSFET without adding a delay before the switching begins?

I'm building a simple 5 W HF CW transmitter, where the power to the final stages is controlled by a P-Channel Power MOSFET, whose gate is connected to a key. I added a simple capacitor between the ...
• 1,307
89 views

### 30MHz signal that could drive a 100W load

I'm seeking an AC source or signal generator for a RF application with the following specifications: Output bandwidth: 0-30MHz Power output: 100W (necessary for sustaining a plasma) The issue I'm ...
• 1,163
1 vote
54 views

### Electrically long loop antenna with homogenous near B field inside antenna loop

I wanted to know is it possible to create a loop antenna that functions in a way like a high frequency helmholtz coil. Because a helmholtz coil is usually made with multiple turns of wire having high ...
• 31
1 vote
39 views

### RF Microstrip trace polygon

I'm designing a board with an RF L-band trace (around 2.150GHz) on the top layer side. I have a clear and unbroken ground plane on the bottom layer of the trace. However, I'm curious to know whether ...
51 views

### P2P communication: maximum range for low power & low bandwidth

I've started a little side project with the goal of tracking my cat's location in real time. To transmit the GPS-data, it seems like I have two options: I can either use cellular communication or (...
• 3
44 views

### Impedance matching T/R switch

I do drive a piezo as transceiver. My transmitter provides square burst around 10Vpp which is too big for simply switching through a diode by dc biasing. I found out that bridge rectifier structure ...
84 views

### Active RF signal repeater

I have two stations, A and B. Station A broadcasts a pure 10MHz sinusoidal signal on air. A ...
• 121
102 views

### Telecom Lines Conducted emissions noise travel

I am seeking an explanation of how conducted emissions on telecom lines are measured. The frequencies of interest are at 150kHz to roughly 850kHz. The size of the unit is 30cm by 30cm by 15cm. The ...
• 554
85 views

### What is inside of a typical RF transformer?

I am tempted to decap this 500 MHz transformer, but guessing the internals are typical and well-known by experts here. I don't understand why many companies don't even spec the two windings' DC ...
• 634
66 views

### Transmitter parasitic drainage [closed]

I have a RF cordless calling/alarm bell which works on batteries. The receiver works with 3x AA batteries and its transmitter works with a 23A (12v) battery. The product works with their function. The ...
• 690